Any advice/experience out there on converting a 2-blade to a 3-blade ?

2-blade McCauley CS prop needs big overhaul, but economics (and good neighbourlynesss) dictate that for a bit extra we can get a brand new MT Propeller MTV12 composite 3-blade (and it weighs the same).

Is it worth the switch ? 2 blade, 76inch rated at 210Hp 2800rpm fitted to a seaplane. 3 blade, 71inch ..... 2600rpm max, will i get any loss of takeoff performance ? Will it be more economical in the cruise ? Will I notice any difference at all ? Apart from beign quieter and sounding less like a Harvard :-(

The most noticeable difference is that with a 3B prop you get classier girlz wanting to fly with you :O

Anyone who says that's irrelevant is an anorak!!

The 5" difference is worth having too ;) But seriously depending on the aircraft the extra ground clearance can definitely be worth it.

All other things being equal (which sometimes they aren't...:}), a three bladed propellor will have slightly better takeoff/climb performance, but the two blade variety will have slightly faster cruise performance.

In addition, if you own a Cessna 182...beware.
I personally know several folks that have replaced their two blade with a three, and have found that there is now slightly more vibration.
Don't know specifically why for the added vibs, but they are not happy campers.
They suggest that if one was to want to switch to a three blade, make a deal with the shop to try it first...then buy.

Quite a lot of people replacing 2B with 3B have had vibration problems, and found they had to get dynamic balancing done.

Why would a 3B prop have better t/o performance?

Yep:

We replaced our 2 blade CSU prop with a 3 blade on our Arrow 2 a coupla years ago when the 2 blade got a serious dink from FOD at a strip not a million miles from here...

The 3 blade was cheaper than 2 blade so how could we refuse.

Performance is exactly the same in all phases of flight but the vibration is a problem.

Despite dynamic balancing, vibration prevents mounting GPS295 (admittedly a heavy unit) on the yoke any more.

Cusco

We bought a 3 blade "Top Prop" from Hartzell (http://www.hartzellprop.com/index2.htm) for our PA32-300 in the summer. Best buy we ever made. Ten times quieter, no vibration, much better ground clearance & 2400hrs or 6yr TBO.
If you order one direct, ask them to mark it AOG, it stops it being held for a couple of days at Heathrow!!

3-bladers can have hangar-rash implications, unless you
a) don't hangar or
b) have your own hangar

would the vibration problem only due to the prop not being balanced? this is an interesting thread.

how about any bph difference given the same RPM with 2B and 3B? more thrust??

nelson

Swapped a 2b for a 3b on a Commander 114, the POH suppliment says that performance is worse.

I think it has a much better t/off and initial climb, cruise is exactly the same.

Much much smoother.

One advantage to a new prop 2 or 3b is that Notice 75 has been changed - you used to have to overhaul every 3 years now its in accordance with the manufacturers specification (if they specify an o/h period if not its still 3 years) in my case thats 6 years, so I defer a big chunk of the star annual.

Another advantage will be that your plane will be more saleable, 3b much sexier!

hmmm ?

Just flew a 3 blade 182T last week and it seemed Ok in terms of usual performance, but the 2 blade 182 I flew prior seemed to climb like a rocket compared, in both cases we had 4 on board, 200ltrs in tanks, 2 blade - 750ft per min no prob, more noise than the 3 blade, but maybe thats what you;d expect, can't recall what the 3 blade did , I think I may have fallen asleep during the climb . :uhoh:

3 blade looks alot smaller, the 2 blade looks huge, less than 2 feet clearance from the tip, maybe that makes a diff ?

I also agree the 2 blade settled into cruise alot faster, 148+ easy, where as the 3 blade seemed to linger around 138, settings were approx 23/23(235) and leaned to 48/50 ltr per hour @<hidden> SL depending on egt/cht

2 blade - 182Q - CONTNTAL / O-470 , MCCAULEY C2A34C204

3 blade - 182T GA-8 - LYCOMING / IO-540-K1A5 , HARTZELL HC-C2YR-1BF/F8475R

The 182Q is also ligter, by approx 300kg, but my "feeling" was it actually went up very quick, and it definitely accelerated into cruise quicker, have not really thought about it in detail until you mentioned this in the post, but maybe someone can tell me different, I am all ears!


cheers

7gcbc

Ho folks, thanks for all the advice ... keep it coming !

Anyone specifically had any dealings with MT Propellers ? Prop balancing/vibration .. is there a pattern to the manufacturers of these ? Or are all 3Bs created equal ;-)

For a nominal amount, it's worth obtaining a copy of this article (http://www.aviationconsumer.com/pub/28_2/misc/4860-1.html), which is fairly informative.

If the vibration stops you mounting a GPS, just imagine what long term damage its doing to the engine, its mountings and the airframe.

It needs sorting, or returning to the vendor.

The article concludes it is a 'guy thang' as in esthetics.

They do look a lot better, don't they!?!

Cusco, I would get that looked at.

FD

Actually the link I provided is just a summary. I believe it costs about US$12 to access the full article (which IMHO is a relatively small amount, for someone considering purchasing a new prop).

Take the Cessna 185 for example.

Takeoff RPM 2650.

With the two blade prop, the tip speed on this particular model nearly reaches mach one (and is very noisey) and as a result of the tip speed, the efficiency of the prop suffers during takeoff versus the three blade, which is a smaller diameter...shorter blades.

During cruise however, the RPM is lower, the tip speed less, so the prop is more efficient versus the three blade because there is only two blades...and less induced drag therefrom.

On some other aircraft however, the difference is rather small...or none at all.

I recently fitted a new three blade to my Arrow. I'm still in two minds about it but some observations so far are:

Smoother operation and less vibration at all power settings

Less cockpit noise

Better initial climb performance (around 1200fpm at mtow) up to about 3000 feet after which it drops off significantly

Much better go-around climb rate

Marginally better ground performance - around 5% shorter take off roll

About a 6% LOSS in overall cruise performance which does seem to increase with altitude, although at max continuous power in straight and level it's actually a few knots faster

Only limitation is to avoid continuous operation below 1950 RPM and less than 15" MAP

Slightly more fuel efficient, although I can't figure out why

Slightly cooler engine operation probably due increased cooling airflow through the cowling

Added drag of the extra blade helps when trying to slow down - steeper approaches and quicker deceleration are very noticeable

No change in glide performance - Arrows glide like man-hole covers with rough edges anyway

The only thing I'm not entirely happy about is the reduced cruise performance, but hopefully with a repaint and speed kit fitted, I might get a bit back.

Let me know if there's any specific questions you have

A

Atlas,

Does fitting a three blader to something like an Arrow require different RPM and MAP settings in the cruise. I ask as with three blades I imagine you would want a slower blade speed so that one blade has less effect on the air for the next blade following it as the gap between the blades is less ("disk solidity" I think they call it).

Or am I barking up the wrong tree?

Cheers,
HWD.

As I understand it (and after a few tinnies on Xmas Eve that's not too clearly) the point of adding more blades to a prop is to absorb/utilise more power (why the most powerful Spits ended up with 5-bladers) and so if you've a relatively low powered engine there is little or no advantage. In my last job we operated Slingsby Fireflies with 160, 200 and 260 hp engines. The 260s had 3 blades and were excellent, the 160s 2 blades and did the job, but the 200s had 3 blades and those with more experience than me said they ruined a perfectly good aircraft as compared to 200s with 2 blades. The general impression I got was that with much less than 250 hp, 2 blades are better.

Beyond a certain HP, somewhere in the few-hundred mark, one has to go to >2 blades otherwise on a prop big enough to absorb the power the tips will end up supersonic and won't work anymore.

The big advantage of more blades is that the prop can rotate slower and so make a lot less noise. This is unlikely to be relevant unless one has a gearbox, though.

High Wing Drifter,

Power settings in the cruise are exactly the same as with a 2B. I don't fly the Arrow that much and can't recall the limitations it had previously but the only one now with the 3B are to avoid continuous operation at less than 15" MAP between 1950 and 2350 RPM. I suspect the limitations would depend on each individual prop/engine combination. So if you wanted to cruise around at 4000 ft at 65% you can still use either 24.8"/2100 or 22"/2400 as per the power setting table(IO-360-C Series)

The only noticeable "disc effect" that I've found so far is in a power off glide - it DOES slow down very quickly although the difference is less noticable if you go full coarse.

A

DB6 statedAs I understand it...the point of adding more blades to a prop is to absorb/utilise more power
And IO540 stateda prop big enough to absorb the power...The big advantage of more blades is that the prop can rotate slower
As an unanitiated, I would have to agree, and comment that the sole purpose of a propellor is to efficiently absorb the available power of the engine.

Any inefficiencies are, well, inefficient, so surely the 3-blade/2-blade scenario is efficiency-driven, with suitable allowance for installation and maintenance cost.

And whether it will fit into the shared hangar

DT

i would refer you to the PPONK website in the US. they have done static thrust comparisons between 2 and 3 blade props from 80" through 90". i have had both 80" and 88" 2 blade props on my 185. the 88" prop is at least 5 knots faster in the cruise and faster acceleration on takeoff.
this was with the 2625 RPM 260Hp engine. i now have the 80" on an IO-520. it should really have an 86" on it. very noisy, but this is not a problem where i live.
The following with apologies to PPONK.
PROPELLER MODEL
STATIC THRUST
At 2600 rpm and full power....
McCauley 2 blade D2A34C58 82" pulled 940 pounds
McCauley 2 blade D2A34C58 86" pulled 1016 pounds
McCauley 2 blade 2A34C66 88" pulled 1019 pounds *
McCauley 3 blade D3A34C403 80" pulled 970 pounds
McCauley 3 blade D3A34C401 80" pulled 1015 pounds
McCauley 3 blade D3A34C401 86" pulled 1183 pounds
McCauley 3 blade D3A34C401 88" pulled 1183 pounds
* Note: The D2A34C58 88" and 2A34C66 88" propellers use the same blades, and would pull the same.

DubTrub,
.........the sole purpose of a propellor is to efficiently absorb the available power of the engine.No.

The purpose of the propeller is to convert engine power into thrust, not absorb it.

When the aircraft is moving, the air in front of the propeller disc area is drawn into the propeller and is accelerated so that the speed of the air behind the propeller is greater than that in front. The acceleration of the "inflow" causes a low pressure in front of the propeller and the "outflow" causes a high pressure behind. The difference in pressure between the inflow and the outflow is the thrust generated by the propeller.

The greater the volume of air that the propeller moves, the greater the cumulative pressure difference.

Therefore an increase in propeller diameter increases the propeller disc area which in turn increases the volume of air.

AS

The Mooney aircraft pilots association have visited this topic many times. The consensus seems to be that 2 bladed props are better on 4 cylinder engines and the 3 bladed on 6 cylinder engines. Owners frequently report that vibration is a problem with 3 bladed props on 4 cylinder engines.

Regards,

Chopperpilot47

chopperpilot47,

I'd be interested in knowing more.

AS

Surely the most efficient prop will have just one blade. That way the blade will be operating in the least disturbed air.

There will be balance problems though :O

So I think that for efficiency alone, a 2B prop has to be the best.

As I said earlier, there are other reasons for going for more blades, e.g. avoiding mach1 on the tips, less noise, better/feasible ground clearance.

I don't see a physical reason why a 3B prop can give better climb while a 2B prop gives better cruise. I bet nobody has tested this with two exactly identical planes where

Plane a) engine is X HP at Y RPM and the prop is 2B

Plane b) engine is X HP at 0.66 Y RPM and the prop is 3B

and both props use identical blades.

:O